Inclusion Criteria:

          -  Age greater than or equal to 18

          -  A pituitary adenoma/carcinoma of any histology

             ° Patients with unresectable tumors that are radiographically (and/or biochemically)
             consistent with a pituitary adenoma may be considered for enrollment without
             pathologic confirmation with approval from the principal investigator.

          -  Progression on imaging following radiotherapy

             ° Patients with pituitary carcinomas in whom there is not felt to be a palliative
             benefit to treatment with radiotherapy are eligible for enrollment without prior
             radiotherapy.

          -  Measurable disease by RANO criteria

          -  At least 4 weeks have elapsed since the patient last received temozolomide and the
             patient must have recovered hematologically from other chemotherapeutics

          -  Karnofsky Performance Status (KPS) greater than or equal to 70

          -  Screening laboratory values must meet the following criteria:

               -  WBC >/= 2000/uL

               -  Neutrophils >/= 1500/uL

               -  Platelets >/= 100 x 10^3/uL

               -  Hemoglobin > 9.0 g/dL

               -  AST/ALT </=3 x ULN

               -  Total Bilirubin </= 1.5 x ULN (except subjects with Gilbert Syndrome, who can
                  have total bilirubin <3.0 mg/dL)

          -  Serum creatinine </= 1.5 x ULN or creatinine clearance (CrCl) >/= 40 mL/min using the
             Cockcroft-Gault formula

          -  Women of childbearing potential (WOCBP) must use appropriate method(s) or
             contraception. WOCBP should use an adequate method to avoid pregnancy for 23 weeks (30
             days plus the time required for nivolumab to undergo five half-lives) after the last
             dose of investigational drug

               -  WOCBP is defined as any female who has experienced menarche and who has not
                  undergone surgical sterilization (hysterectomy or bilateral oophorectomy) or who
                  is not postmenopausal. Menopause is defined clinically as 12 months of amenorrhea
                  in a woman over 45 in the absence of other biological or physiological causes.
                  Women who are not of childbearing potential are not required to use contraception

               -  Women of childbearing potential must have a negative serum or urine pregnancy
                  test upon study entry

          -  Men who are sexually active with women of childbearing potential must use adequate
             contraception upon study entry until 31 weeks after the last dose of study treatment.
             Men who are surgically sterile or azoospermic do not require contraception.

        Exclusion Criteria:

          -  A corticosteroid requirement of greater than 4mg per day of dexamethasone (or an
             equivalent dose). NOTE: Patients requiring a physiologic replacement dose of
             corticosteroids, who may require stress dose corticosteroids, due to adrenal
             insufficiency are permitted onto this trial

          -  Active, known, or suspected autoimmune disease within the past 2 years. NOTE: Subjects
             are permitted to enroll if they have vitiligo, type I diabetes mellitus, residual
             hypothyroidism due to autoimmune condition only requiring hormone replacement,
             psoriasis not requiring systemic treatment, or conditions not expected to recur in the
             absence of an external trigger

          -  Patients should be excluded if they have had prior systemic treatment with a CTLA-4
             antibody. Prior treatment with PD1 or PD-L1 antibodies are permitted as long as the
             patient did not experience serious toxicities requiring treatment discontinuation
             related to prior PD-1 or PD-L1 therapy

          -  Patients should be excluded if they have a known history of testing positive for
             hepatitis B virus surface antigen (HBV sAg) or hepatitis C virus antibody (HCV
             antibody) indicating acute or chronic infection

          -  Patients should be excluded if they have a known history of testing positive for human
             immunodeficiency virus (HIV) or known acquired immunodeficiency syndrome (AIDS)

          -  History of allergy to study drug components

          -  History of severe hypersensitivity reaction to any monoclonal antibody

          -  Women who are pregnant or breast-feeding

          -  Inability to undergo radiographic surveillance